Cold seal lamp pressure regulation



May 27, 1969 L, R. GALLAGHER ETAL 3,447,030

COLD SEAL LAMP PRESSURE REGULATION Filed Feb. ze, 19e? Sheetl hmm.

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May 27, 1969 L.. R. GALLAGHER ETAL 3,447,030

COLD SEAL LAMP PRESSURE REGULATION med Feb. ze, 1967 A sheet. of 2 85g lY 5', L* "FMT ql CESIUM VPOR l l' lI Il l' I: 2`| N II k ELECTRODE 2OPRESSURE CONTROL SYSTEM United States Patent O 3,447,030 COLD SEAL LAMPPRESSURE REGULATION Lee R. Gallagher, Altadena, Calif., and Peter D.Lenn, Arlington, Va., assignors to Electro-Optical Systems, Inc.,Pasadena, Calif., a corporation Vof California Filed Feb. 28, 1967, Ser.No. 619,391 Int. Cl. H011 13/28, 17/26 U.S. Cl. 315-108 7 ClaimsABSTRACT OF THE DISCLOSURE This invention particularly relates to arcdischarge devices of the type disclosed in copending U.S. patentapplication Ser. No. 501,452 filed Oct. l22, 1965, now abandoned, andassigned to the present assignee, this device being of the type whereinthe arc gap electrodes are mounted within an envelope which defines atubular volume between the envelope and each of the electrodes, each ofthese tubular volumes containing a quantity of the discharge material inits liquid state. Each of the t-hus formed tubular bodies of liquid isheld by capillary forces and acts as a thermal barrier extending betweenthe annular liquid-vapor interface in the vicinity of the arc and theenvelope-electrode seal, the length and crosssectional area of theliquid tube being adequate to maintain a substantial temperaturedifference between the envelope seals and the parts of the device in thevicinity of the arc. Thus, the temperature of the device in the vicinityof the arc may be kept high with a correspondingly high vapor pressure,and the seals will be cool because of the difference established by thethermal barrier:

By utilizing a tubular volume of sutiicient length, the temperaturegradient can be great enough so that ordinary mechanical envelope sealsmay be utilized.

The aforementioned arc discharge device structure was developed toprovide more eflicient physical and thermal insulation of the envelopeseals from the vaporized discharge material, thereby enabling operationat high vapor pressures and power outputs wit-h long seal life.

The present invention is directed toward a technique for controllablychanging the position of the annular vapor-liquid interface in the abovediscussed structures without contacting the discharge material vapor,thereby enabling the device operator to conveniently control, changeand/or monitor the arc pressure. In accordance with the presentinvention concepts the liquid discharge material is supplied to thedevice envelope from a pressurized storage container, pressurization ofthe storage container being controlled by means of a suitable pressurecontrol system. Thus, for example, by increasing the pressure within thestorage container more of the liquid discharge material is forced intothe device envelope to move the annular liquid-vapor interfaces closerto the hot end of the electrodes, t-hereby increasing the vaporpressure.

Accordingly, it is an object of the present invention to provide animproved arc discharge device.

It is a primary object of the present invention to provide an improvedarc-discharge device utilizing a liquid discharge material and in whichthe position of the liquidvapor interface during operation can becontrollably changed.

It is also an object of the present invention to provide an improvedvapor-electric tube.

It is another object of the present invention to provide an improvedvapor-electric tube wherein the arc pressure may be convenientlycontrollably varied.

It is a further object of the present invention to provide an improvedvapor-electric tube wherein the arc pressure -may be convenientlymonitored.

It is a still further object of the present invention to provide animproved vapor-electric tube wherein the discharge material is fed inliquid form to the device envelope.

It is yet another object of the present invention to provide an improvedvapor-electric tube wherein the discharge material is fed in liquid formto the device envelope from a pressurized storage container.

It is also an object of the present invention to provide an improvedvapor-electric tube of the type described wherein the pressure withinthe storage container for the liquid discharge material is selectivelyvariable.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages thereof Iwill be better understood(from the following description wherein FIGURE 1 represents thepresently preferred embodiment of the invention and FIGURE 2 is analternate embodiment of the device of FIGURE l. It is to be expresslyunderstood, however, that the drawing is for the purpose of illustrationand description only, and is not intended as a definition of the limitsof the invention.

FIGURE l shows a cross-sectional view, partly in block form, of a deviceembodying this invention.

The arc discharge device primarily comprises a tubular envelope 10having two rod type electrodes 20 and 30 disposed coaxially therein. Theillustrated embodiments are intended for use with cesium as thedischarge material, and accordingly the envelope 10 is made ofcrystalline alumina, a material which is inert to cesium and which isICC .substantially transparent to visible light and to light in theinfrared and near infrared region.

The electrode 20 defines two coaxial portions, a main body portion 22and a reduced diameter tip portion 24 which terminates in a pointed end25. The electrode 30 similarly defines a main body portion 32 and areduced diameter tip portion 34 terminating a pointed end 35.

The main body portions 22 and 32 of the electrodes 20 and 30 projectthrough the open ends of the envelope 10 and terminate in electricalterminals 12 and 14 to I.vvhich are connected one end of electricalleads 15 and 17. The other ends of the electrical leads 15 and 17 areconnected to a suitable power source B.

The electrodes 20 and 30 are disposed with their pointed ends separatedby a suitable gap for creating the desired discharge arc, the electrodes20 and 30 of the illustrated embodiment being made of tungsten.

Mechanical end seals 18 and 19 are provided to seal the ends of theenvelope 10 about the electrodes 20 and 30, the seals being fabricatedof steel. The seals are provided with suitably sized circular openingsthrough which the main -body portions of the electrodes are press fittedand then soldered to complete the seal therebetween. A pair of nitrilerubber O-rings 41 and 42 are provided to complete the seal to theenvelope 10.

The diameter of the -main body portions 22 and 32 of the electrodes 20and 30 is a predetermined amount less than the inside diameter of thetubular envelope 10 so that the liquid discharge material will becontained in the resulting tubular volume by capillary forces. Thedrawing is not intended to be to scale and the tubular bodies of liquidcesium in the envelope are shown to be relatively thick in order toclearly depict the meniscuses at the liquid- Vapor interfaces. The mainbody portions o f the electrodes may be provided with radially extendinginsulating projections (not shown) to maintain the coaxial alignment ofthe electrodes within the envelope.

Closed receptacles 50 and 60 each contain a quantity of the dischargematerial in its liquid state, for example cesium. A feed pipe 51interconnects the receptacle S0 with one end of the envelope 10 forfeeding the liquid cesium into the tubular volume surrounding the mainbody portion 22 of the electrode 20, a feed pipe 61 interconnecting thereceptacle 60A with the other end of the envelope 10 for feeding theliquid cesium into the tubular volume surrounding the main body portion32 of the electrode 30. The feed pipes 51 and 61 pass through suitableapertures in the respective end seals 18 and 19. Alternatively, a singleclosed receptacle can be used in conjunction with a single feed pipe andan insulated joint (capillary connection) coupling the reservoir ofliquid discharge material to both ends of the tube. This alternativeembodiment is shown in FIGURE 2 wherein 70 is the single closedreceptacle and 71 is the single 'feed pipe connected to capillary feedpipes 72 and 73. Electrically, the discharge device is operated suchthat the resistance path through the arc is much lower than theresistance path through the liquid discharge material in the feed pipes.The resistance of the liquid discharge material can be increased bymaking the capillary feed pipes of smaller diameter and/r increasingtheir length. In FIGURE 2, the diameter of pipes 72 and 73 have beenincreased for purposes of illustration, but it should be understood thatthey are meant to represent capillary connections. However, it ispresently preferred to use separate receptacles and feed pipes toabsolutely insure electrical isolation.

A pressure control systems, generally indicated by the reference numeral55, is provided to pressurize the receptacles 50 and 60 with a cold gasatmosphere, such as argon or helium for example. The pressure controlsystem 55 is adjustable so that the gas pressure within the receptacles50 and 60 can be controllably varied. By increasing the ambient gaspressure within the receptacles 50 and '60, more of the liquid cesiumwill be forced through the feed pipes 51 and 61 and into the ends of theenvelope 10, thereby moving the annular liquid-vapor interfaces closerto the electrode tips, which results in an increase in the vaporpressure. Thus, use of the pressure control system to pressurize theliquid metal supply enables selective control of the position of theliquid-vapor interface during device operation. Hence, the arc pressuremay be controlled, changed and/or monitored during the device operation.

To begin device operation, the pressure control system 55 is adjusted tocharge the tube 10 with a predetermined amount of cesium. An electricalpotential is applied across the terminals y12 and 14 to create an arcacross the gap between the pointed electrode ends 25 and 35, The heatfrom the arc vaporizes the cesium which ionizes and creates aself-sustaining discharge arc. Upon vaporization some of the cesiumcondenses on the relatively cool surfaces of the alumina envelope andthe main body portions olf the electrodes and 30, the condensed liquidbeing held in the tubular volume between the envelope( and electrodemain body portions by capillary forces. Much of the heat generated fromthe arc will be conducted by the liquid cesium in the tubular volumethrough the walls of the envelope 10 to the ambient atmosphere.Suflicient heat is removed so that the end seals 18 and 19 remainrelatively cool, yet the temperature in the arc region remainssufiicently high to prevent condensation of the cesium.

Thus there has been described a system for controlling the position ofthe annular vapor-liquid interface in an arc discharge device of thetype wherein the arc gap electrodes are mounted within an envelopedefining a tubular volume between the envelope and each of theelectrodes, these tubular volumes containing discharge material in itsliquid state with the liquid held by capillary forces. Although thehereinabove presented structural embodiment utilizes a cylindricaltubular envelope and rod type electrodes, any other envelope andelectrode configurations may be utilized which will produce a tubularsheath of liquid discharge material about the electrodes and ofsufficient length to provide the desired temperature gradi ent. Also,the present invention system concept is applicable for use with anysuitable vaporizable discharge material that can be convenientlycontained in liquid form, and those skilled in the art will appreciatethe various structural materials suitable for use with a given dischargematerial. Furthermore, it is contemplated that the receptacles 50 and60, and the feed pipes 51 and 61 be provided with controlla-ble heatingmeans to maintain them at the temperature necessary to hold the thereincontained discharge material in its liquid state.

Thus, although the invention has been described with a certain degree ofparticularily, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the combinationand arrangement of parts may be resorted to without departing from thespirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. In an arc discharge device of the type wherein an elongate arc gapelectrode is mounted within an elongate portion of an envelope to definea tubular volume therebetween, the tubular volume containing a quantityof discharge material in its liquid state to form an annularliquid-vapor interface during device operation, the improvementcomprising:

(a) a closed receptacle containing a quantity of said discharge materialin its liquid state;

(b) feed pipe means connecting said receptacle with said tubular volumein the elongate portion of said envelope;

(c) means -for pressurizing said receptacle to force some of said liquiddischarge material through said feed pipe means and into said tubularvolume; and

(d) means for controlling the pressure within said receptacle to therebycontrol the amount of said liquid discharge material within said volumeand hence for controlling the position of the liquid-vapor interfaceduring device operation.

2. In an arc discharge device as specified in claim 1, wherein theenvelope is of cylindrical tubular configuration and said arc gapelectrode is a rod coaxially mounted therein.

3. In an arc discharge device of the type wherein a pair of elongate arcgap electrodes are coaxially mounted in spaced apart relationship inseparate elongate portions of a tubular envelope to define a tubularvolume between each of said electrodes and the adjacent portions of saidenvelope, each tubular Volume containing a quantity of dischargematerial in its liquid state to form an annular liquid-vapor interfaceduring device operation, the improvement comprising:

(a) a closed receptacle containing a quantity of said discharge materialin its liquid state;

(b) feed pipe means connecting said receptacle with the tubular volumein each of said separate elongate portion of said envelope;

(c) means for pressurizing said receptacle to force some of said liquiddischarge material through said tfeed pipe means and into said tubularvolumes; and

(d) means for controlling the pressure within said receptacle to therebycontrol the amount of said liquid discharge material within said volumesand hence for controlling the position of the liquid-vapor interfacesduring device operation.

4. In an arc discharge device of the type wherein a pair of elongate arcgap electrodes are coaxially mounted in spaced apart relationship inseparate elongate portions of a tubular envelope to define a tubularvolume between each of said electrodes and the adjacent portions 0f saidenvelope, each tubular volume containing a quantity of dischargematerial in its liquid state to form an annular liquid-vapor interfaceduring device operation, the irnprovement comprising:

(a) a first closed receptacle containing a quantity of said dischargematerial in its liquid state;

('b) a second closed receptacle containing a quantity of said dischargematerial in its liquid state;

(c) first feed pipe means connecting said first receptacle With thetubular volume in one of said elongate portions of said envelope;

(d) second feed pipe means connecting said second receptacle with thetubular volume in the other of said elongate portions of said envelope;

(e) means for pressurizing said first and second receptacles to forcesome of said liquid discharge material through said first and secondfeed pipe means and into said tubular volumes; and

(f) means -for controlling the pressure within said first and secondreceptacles to thereby control the amount of said liquid dischargematerial within said volumes and hence for controlling the position ofthe liquidvapor interfaces during device operation.

5'. In an arc discharge device as specified in claim 3, wherein saidenvelope is of cylindrical tubular configuration and said arc gapelectrodes are rods coaxially mounted therein.

6. In an arc discharge device as specified in claim 4, wherein saidenvelope is of cylindrical tubular configuration and said arc gapelectrodes are rods coaxially mounted therein.

7. The arc discharge device of claim 3 wherein said feed pipe meanscomprises a single conduit connected to said receptacle, said conduitconnected at the end opposite from said receptacle to first and secondcapillary conduits, each of said capillary conduits being connected toone end of said envelope for admitting liquid discharge material to saidtubular volumes.

References Cited UNITED STATES PATENTS 7/ 1911 Weintraub s 313-43 X2/1968 Rogers et al. 313-231 X U.S. Cl. X.R.

